1) Apical periodontitis is caused by microbial infection of the root canal system, usually after pulp necrosis. Bacteria are the primary cause, though fungi and archaea have also been implicated. 2) Bacteria enter the root canal system through caries, cracks, restorative procedures, or periodontal disease. They can also travel through dentinal tubules or directly expose the pulp. 3) Successful endodontic treatment aims to prevent or resolve apical periodontitis by thoroughly debriding and disinfecting the root canal system.

1. Endodontic Microbiology
Dr. Mohammed Alshehri BDS, AEGD, SSC-Resto, SF-DI

2. Microbial Causation Of Apical Periodontitis
• Apical periodontitis is an inflammatory disease of
microbial etiology primarily caused by infection of the
root canal system
• Endodontic infections usually develop after pulpal necrosis
or in cases in which the pulp was removed for treatment.
Although fungi and most recently archaea and viruses have
been found in endodontic infections, bacteria are the major
microorganisms implicated in the etiology of apical
periodontitis.

3. The ultimate goal of the endodontic treatment is either to
prevent the development of apical periodontitis or to
create adequate conditions for periradicular tissue
healing.

4. Portals of Entry to the Pulp
• Caries
• Trauma-induced fractures
• Cracks
• Restorative procedures
• Scaling and root planing
• Attrition
• Abrasion
• Gaps in the cementoenamel junction at the cervical root surface
• Dentinal tubules
• Direct pulp exposure
• Periodontal disease
• Anachoresis

5. Dentinal Tubules
• Permeability of normal dentin dictated by its tubular structure.
• Dentin permeability is increased near the pulp because of the larger
diameter and higher density of tubules.
• Dentinal tubules traverse the entire width of the dentin and have a
conformation of inverted cones, with the smallest diameter in the
periphery, near to enamel or cementum (mean of 0.9 μm).
• The smallest tubule diameter is entirely compatible with the cell
diameter of most oral bacterial species, which usually ranges from 0.2
to 0.7 μm.

6. Dentinal Tubules
• Bacterial movement is restricted by
• Outflow of dentinal fluid
• Odontoblastic processes
• Mineralized crystals
• Immunoglobulin's in the tubules.

7. Dentinal Tubules
• Facultative gram positive bacteria
Propionibacterium
Eubacteruim
Arachnia
Lactobacilli
Bifidobacterium
Actinomyces
• Some of gram negative bacterial such as Bacteroides

8. Direct Pulp Exposure
• Direct exposure of the dental pulp to the oral cavity is the
most obvious route of endodontic infection.
• Caries is the most common cause of pulpal exposure
• Exposed pulps will undergo inflammation and necrosis
and become infected.
• The time elapsed between pulp exposure and infection of
the entire canal is unpredictable, but it is usually a slow
process.

9. Periodontal Disease
• Microorganisms in subgingival biofilms associated with
periodontal disease could reach the pulp by the same
pathways that intracanal microorganisms reach the
periodontium and thereby could exert harmful effects on
the pulp.
• Pulpal necrosis as a consequence of periodontal disease
only develops if the periodontal pocket reaches the apical
foramen, leading to irreversible damage to the main blood
vessels that penetrate through this foramen.

10. Anachoresis
• Anachoresis is a process by which microorganisms are
transported in the blood or lymph to an area of tissue
damage, where they leave the vessel, enter the damaged
tissue, and establish an infection.
• There is no clear evidence showing that this process can
represent a route for root canal infection.

11. Anachoresis
• Bacteria could not be recovered from unfilled root canals
when the bloodstream was experimentally infected, unless
the root canals were overinstrumented during the period of
bacteremia, with resulting injury to periodontal blood
vessels and blood seepage into the canal.
• Although anachoresis has been suggested to be the
mechanism through which traumatized teeth with
seemingly intact crowns become infected, current evidence
indicates that the main pathway of pulpal infection in these
cases is dentinal exposure as a result of enamel cracks.

12. Types of endodontic infections
• Intraradicular infection
– Primary intraradicular infection : initial infection or
“virgin” infection
– Secondary intraradicular infection : during treatment,
between appointments, or even after root canal filling
– Persistent intraradicular infection : This is also termed
recurrent infection. Involved microorganisms are
remnants of a primary or secondary infection

13. Types of endodontic infections
Primary intra radicular infection
Gram negative bacteria, Fusobacterium, Gram positive
bacteria, Actinomyces
Secondary / persistent intra radicular infection
Streptococci, Root canal treated teeth Enterococcus
faecalis
Persistent intraradicular infection
fewer species than primary infections,and gram-positive
facultative or anaerobic bacteria are predominant. Fungi can
also be found in frequencies significantly higher when

14. Types of endodontic infections
• Persistent and secondary infections are for the most part
clinically indistinguishable and can be responsible for
several clinical problems, including persistent exudation,
persistent symptoms, interappointment flare-ups, and
failure of the endodontic treatment characterized by a
posttreatment apical periodontitis lesion.

15. Types of endodontic infections
• Extraradicular infection
– Extraradicular infection is characterized by microbial invasion of
and proliferation in the inflamed periradicular tissues and is
almost invariably a sequel to intraradicular infection.
Extraradicular infection can be dependent on or independent of
the intraradicular infection
Actinomyces

16. Endodontic Microbiota
• Gram negative bacteria
– Treponema
– Fusobacterium
• Gram positive bacteria
– Streptococcus
– Actinomyces

17. Available nutrients for bacteria
• Necrotic pulp tissue
• Proteins and glycoprotein's from tissue fluids
• Components of saliva
• Products of other bacteria

18. Resistance of Oral Microbes to Medicaments
• Enterococci has been shown to be relatively resistant to
Ca(OH)2 and occur in high frequency in retreatment cases

19. Treatment of Endodontic Infections
• The key to successful treatment of endodontic infections is
removal of the reservoir of infection (necrotic tissue,
bacteria, and bacterial by-products) by the following
procedures:
Debridement of the root canal system by mechanical instrumentation
Root canal irrigation
Intracanal medication Ca(OH)2
Drainage